This invention relates generally to a hydraulic vehicle transmission control system for selectively actuating a hydraulically-operated clutch and, more particularly, to means for dampening or modulating the directional controls of the vehicle.
Heavy-duty earthmoving vehicles, such as loaders or bulldozers, employ extensive hydraulic circuitry to obtain desired operational control and achieve effective performance. Sophisticated circuits including specially designed pressure modulating and directional control valves and pressure accumulators are often integrated into these hydraulic circuits to obtain specific functions, desired responses and operating characteristics so as to achieve maximum performance of the vehicle and the loader mechanism.
For example, pressure accumulators can be introduced to obtain the necessary response or pressure displacement required to engage clutch plates, brake bands or other related control means and hydraulic control valves can be used in combination with a spring-biased pressure regulator to obtain dual modulation for a transmission control system.
In the past, when a vehicle was used as a bulldozer, it was customary to integrate a spring-loaded accumulator into the first forward speed control circuit to cushion transmission clutch loads. Pressure fluid would be diverted into the high pressure end of the accumulator to shift the accumulator piston after forcefully overcoming the biasing spring load. Through the sequential shifting of the piston, delayed buildup of fluid pressure and driving engagement of transmission clutches was accomplished. Thus, engagement and shock loads generated by rapid transmission clutch engagements under heavy loads were effectively modulated.
Presently, when the forwardly disposed bucket of a loader is elevated and filled with heavy material, rapid engagement of the reverse speed clutches and quick acceleration to a reverse drive can cause the rear of the vehicle to raise up and pivot about the front idler even when the vehicle is heavily counterbalanced. It therefore becomes highly desirable to provide within the control circuitry a means for regulating the engagement of the various drive clutches so that the rate of acceleration can be regulated and kept within safe limits so as to greatly inhibit the rocking of the vehicle and reduce stress on components.
If an accumulator were connected to the reverse speed directional port of the transmission control valve to cushion the engagement of the reverse speed clutch, it would maintain optimal vehicle stability when and if sudden engagement of the reverse speed clutch were effected with the bucket elevated and fully loaded. It is evident then that a relatively simple accumulator incorporated into the transmission control circuits making extended and improved use of the vehicle possible would be advantageous.